[vtkusers] flat shading in vtk

[David Doria]

On Wed, Jan 27, 2010 at 10:35 AM, David Gobbi <david.gobbi at gmail.com> wrote:
> On Wed, Jan 27, 2010 at 7:54 AM, David Doria <daviddoria+vtk at gmail.com> wrote:
>> On Mon, Jan 25, 2010 at 4:55 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>> Oh, that's what you meant. Set "Ambient" to 1, and set "Diffuse" and
>>> "Specular" to 0.  That should completely eliminate all directional
>>> lighting.
>>>
>>>   David
>>>
>>>
>>> On Mon, Jan 25, 2010 at 2:43 PM, Liam Kurmos
>>> <quantum.leaf at googlemail.com> wrote:
>>>> On Mon, Jan 25, 2010 at 9:18 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>> Try property->SetInterpolationToFlat().
>>>>
>>>> That produced flat shading, but the shading is still dependant on the
>>>> surface normals. (just not interpolated/smoothed like gourad).
>>>> What i want is a constant colour. Obviously that will mean object
>>>> won't look very 3d but that is what i want in this case (i want to
>>>> measure how much area of an object i can see by how many pixels of its
>>>> colour i can count in the render window)
>>>>
>>>> I thought property->ShadingOff()/SetShading(0) sounded promising but
>>>> they don't seem to be having any effect (i have a coloured sphere and
>>>> it still gourad shaded).
>>>>
>>>> Also, I managed to turn the lights of with
>>>> ren1->SetAutomaticLightCreation(0);
>>>> but then i discovered there isn't an 'emissive color' property in vtk.
>>>>
>>>> Liam
>>>>
>>>>
>>>>
>>>>>
>>>>>  David
>>>>>
>>>>> On Mon, Jan 25, 2010 at 2:05 PM, Liam Kurmos
>>>>> <quantum.leaf at googlemail.com> wrote:
>>>>>> Is there an easy way to disable shading in vtk?
>>>>>> I want all pixels drawn for a polygon to be constant colour,
>>>>>> independent of surface normals.
>>>>>>
>>>>>> I'm going to try having only an emissive color and turning off a
>>>>>> lights, but now i'm stuck turning off the default light.
>>>>>>
>>>>>> ren1->RemoveAllLights();
>>>>>>
>>>>>> doesn't seem to be having any effect.
>>>>>>
>>>>>> searches like
>>>>>>
>>>>>> "site:vtk.org/Wiki/VTK/Examples getLights"
>>>>>>
>>>>>> are coming up blank, so i wonder if i'm on the right track.
>>>>>>
>>>>>> any help much appreciated,
>>>>>>
>>>>>>
>>>>>> Liam
>>
>> Here is a demo:
>>
>> http://www.vtk.org/Wiki/VTK/Examples/Visualization/FlatShading2
>>
>> SetDiffuse(0) and SetSpecular(0) make the actor black, but adding
>> SetAmbient(1) makes it so bright that it is just a white window!
>> SetAmbient(.5) seems to do the trick.
>>
>> Thanks,
>>
>> David
>
> David, let me explain.
>
> The background in your example is white.  The actor is white, too.  So
> of course, if the ambient light coefficient is set to 1.0, then
> everything will be white.
>
> Please change your example so that the actor is some color other than
> white, and then you can set ambient to "1.0".
>
> Also, this example should not be called "Flat Shading".  It should be
> called "No Shading" or "No Directional Lighting".  Flat shading has a
> very specific definition in computer graphics:
> http://en.wikipedia.org/wiki/Shading#Flat_vs_smooth_shading
>
>   David
>

You're right. It's changed. I thought the actors were grey by default
- guess not.

http://www.vtk.org/Wiki/VTK/Examples/Visualization/NoShading

Thanks,

David